If a + b + c = 4 0 0 , where a , b and c are non-negative numbers, then what is the maximum possible value of
2 a + b + 2 b + c + 2 c + a = ?
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Thank you for sharing your solution.
Due to symmetry, a=b=c.
By using that we get 60,which is the maximum
value in the option.
Therefore, 60 is the answer.
Your logic is wrong. The min/max of a function does not always occur when all its variables are equal. See Inequalities with strange equality conditions .
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But the maximum value in the option is 60.
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What if 60 isn't given as an answer?
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@Steven Jim – Then I would view the solution. XD
@Steven Jim – When it comes to competitive objective exams, this method is good
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@Genis Dude – "When it comes to competitive objective exams" doesn't mean you should spam the answer that way. Considering that Brilliant is a place to "learn", it's advisable to give good solutions. Yes, the method is good, but what if there are no "possible answers" for you to choose?
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@Steven Jim – Then, I would try and I'm not spamming, this is a good method used by many maths nerds.
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For a , b , c > 0 , we can apply the Cauchy-Schwarz inequality .
( 2 a + b + 2 b + c + 2 c + a ) 2 ⟹ 2 a + b + 2 b + c + 2 c + a ≤ ( 1 2 + 1 2 + 1 2 ) ( ( 2 a + b ) 2 + ( 2 b + c ) 2 + ( 2 c + a ) 2 ) ≤ 3 ( 2 a + b + 2 b + c + 2 c + a ) = 9 ( a + b + c ) = 3 6 0 0 ≤ 6 0